Ever since the factories of the Industrial Revolution gave birth to the world's earliest mechanical fans to cool workers who toiled in their hot, steamy environs, much effort has been devoted to improving the cooling efficiency of subsequent generations of mechanical fans. Fans intended for domestic use have, over the years, undergone many modifications which have shared the common goal of providing improved cooling. Although basic fan design has appeared to have changed little since the early mechanical fans, the often subtle differences in such features as rotor arrangement, blade configuration and housing shape in the prior art have all been effected in an attempt to provide improved air circulation by the fan and hence, increased cooling of the fan's intended environment.
Some of the prior art has focused on modifying various features of either the fan impeller or housing or both to affect the flow pattern or velocity of the air flowing through the fans, thereby maximizing efficiency. For example, Borchers, in U.S. Pat. No. 3,169,694, discloses a casing for a propeller fan having a bell-shaped mouth or inlet wherein the fan blades are positioned significantly downstream of the inlet so that the fan produces a controlled vortex flow of air having a predetermined angular velocity to move a maximum quantity of air through the fan in any particular time. In U.S. Pat. No. 2,154,313, McMahan discloses a propeller fan which has a cylindrical housing with an outwardly flaring edge which provides an intake orifice for guiding air from outside the casing into the fan blades prior to distribution by directing vanes. Neither of these fan housings, however, directs air into the fan in a manner which promotes laminar flow or reduces noise.
Katagiri et al in U.S. Pat. No. 4,189,281 disclose a housing or shroud for an axial flow fan which may be varied in shape to regulate the flow of air into the intake side of the fan. This fan, however, relies on the combination of both a shroud and the insertion of auxiliary fan blades within the shroud to achieve increased air flow from the fan while decreasing operating noise levels.
Structure to increase fan operating efficiency in the form of a shroud or annulus surrounding a propeller fan is disclosed by Herrman in U.S. Pat. No. 2,536,130. The shroud or annulus includes a rounded edge on the upstream side of the fan which results in a gradual increase in the velocity of the air moved by the fan blade tips. The width of the shroud relative to the size of the fan discharge orifice must be carefully controlled to achieve the operating efficiency of this fan. Although the arrangement and shroud configuration proposed by Herrman may result in a more efficient fan operation than other prior art fan designs, it still falls short of the efficiencies desired in a domestic fan intended to cool an entire room. The Herrman fan design, moreover, does not include structure which will cause a reduction in the noise which typically accompanies the operation of this type of fan.
An apparatus including a shroud structure which forms a wind gathering venturi and provides a streamlined wind collecting inlet and exhausts air with a minimum of turbulence is disclosed by Eckel in U.S. Pat. No. 4,140,433. This apparatus, however, is intended for use as a power-generating wind turbine capable of generating substantially more power than a conventional windmill and, as disclosed, is highly unsuitable for use as a portable household fan of the type commonly employed for cooling.
The prior art, therefore, fails to disclose a portable fan which operates aerodynamically, in a substantially noise-free manner, to efficiently move air in a laminar flow pattern throughout the surrounding environment to effectively cool this space.